The Serbian First Army was a Serbian field army that fought during World War I.

Following the Austro-Hungarian invasion of Serbia, the First Army was put under the command of General Živojin Mišić, who came out of retirement to do so. In December 1914 the First Army won a decisive victory against Austria-Hungary at the Battle of Kolubara that resulted in the humiliating expulsion of the Austro-Hungarian Army from Serbia at the end of 1914, which saw Mišić promoted to Field Marshal.

When the second combined German, Austro-Hungarian, and Bulgarian invasion force attacked Serbia, Mišić was in favor of halting and making a final stand against the Central Powers forces. However, he was over-ridden by King Peter I and the Serbian government, and the First Army took part in the epic retreat of the Serbian Army through the Albanian mountains during the winter of 1915 and 1916.

Misic was recalled to command the First Army in September 1916 initially at Monastir and then at Thessaloniki. The First Army took part in the Allied Vardar Offensive of 1918 that effectively knocked Bulgaria out of the war.